In the prior art, there are several methods of obtaining white light by processes different from the phenomenon of black body radiation, i.e. incandescence. Methods based on the use of organic phosphors excited in the ultraviolet range (UV) and based on inorganic phosphors doped with transition metal ions or rare earth metal ions dominate among them.
European Patent Application EP 1 475 380 A1 discloses the use of organic compounds for generating white light, on the basis of the phenomenon of electroluminescence. The disadvantage of this solution is the lack of stability of light emission of a particular colour and gradual change of light colour towards yellow, and high wear of OLEDs, which makes the solution according to this invention not meet the expectations put upon modern lighting.
US Patent Application US 2005/0253113 A1 discloses the use of glasses doped with ions of lanthanides excited in the UV range to the range of blue light for obtaining white luminescence constituted of a plurality of narrow spectral lines occurring in the blue, green and red range of the electromagnetic spectrum. The colour of the such obtained light makes only impression of white light—the light is generally considered as “cold” and unfriendly in perception.
US Patent Application No US 2011/0309303 A1 discloses the use of oxyfluoride matrices co-doped with lanthanide ions for generating white light using optical pumping with infrared radiation. Emission of white light by means of matrices according to this invention uses the phenomenon of up-conversion through a combination of spectrally narrow emission lines characteristic for f-f transitions of lanthanide ions.
However, U.S. Pat. No. 7,088,040 B1 discloses the use of the phenomenon of up-conversion in matrices made of NaYF4 doped with Er and Yb, of YLiF4 doped with Tm and Yb, of YF3 doped with Tm and Yb, and of YF3 doped with Er and Yb ions. The radiation in this invention is absorbed by one of the dopant ions—the so called sensitizer (here Yb ions), and the radiation characteristic of the emitting lanthanide ions (the so called activator, here Er and Tm ions) on the third degree of oxidation is obtained by multiphoton processes, while this radiation is characterised by narrow spectral emission lines.